Probably sent chills up the spine of the one who understood in English. That's how many would distinguish the true prophecy from the false in pentecostal circles. Even when it disagrees with Scripture as has happened on many occasions with the imfamous "Hen-Master" (alias Benny the Hen). They will swallow just about anything from a self-appointed anointed guru! I know --- been there and done that!
Yes, there need to be believers around who can candidly discern what is happening. Tongues of themselves are neutral, like the technology of radio broadcasting. The use they are put to is not neutral; either it can be used by evil spirits or blessed ones.